Notes Receivable (Disclosure of Delinquency Status of EnerBank's Consumer Loans) (Details) (USD $)
In Millions
Sep. 30, 2011
Dec. 31, 2010
Total Outstanding$ 439[1]$ 386[1]
EnerBank USA [Member]
  
Past Due 30-59 Days1 
Past Due 60-89 Days1 
Past Due Over 90 Days  
Total Delinquent2 
Current437 
Total Outstanding$ 439$ 386
[1]1 Includes current portion of notes receivable of $16 million at September 30, 2011 and $11 million at December 31, 2010.